U.S. patent number 5,595,799 [Application Number 08/572,596] was granted by the patent office on 1997-01-21 for coinjection molding of decorative preforms and containers produced from such preforms.
This patent grant is currently assigned to DTL Technology Limited Partnership. Invention is credited to Martin H. Beck, Robert Caldicott, John H. Muszynski.
United States Patent |
5,595,799 |
Beck , et al. |
January 21, 1997 |
Coinjection molding of decorative preforms and containers produced
from such preforms
Abstract
A process for injection molding a multi-colored article in an
injection mold, in which a) a desired initial quantity of a
first-colored material is metered to a first desired portion of the
cavity; b) a desired quantity of a second-colored material is
supplied to the cavity, contiguously with the first-colored
material, and is metered to a second desired portion of the cavity.
The location of the first and second desired portions within in the
cavity being controlled by providing the first and second-colored
materials with appropriate melt viscosities and controlling the
temperature and rate of supply of the first and second-colored
materials. A multi-colored preform formed by the process that is
suitable for blow molding a multi-colored container, and a
multi-colored container blow molded from such a preform are also
provided.
Inventors: |
Beck; Martin H. (Amherst,
NH), Caldicott; Robert (Nashua, NH), Muszynski; John
H. (Auburn, NH) |
Assignee: |
DTL Technology Limited
Partnership (Amherst, NH)
|
Family
ID: |
24288544 |
Appl.
No.: |
08/572,596 |
Filed: |
December 14, 1995 |
Current U.S.
Class: |
428/35.7;
264/255; 264/297.2; 264/328.14; 264/328.15; 264/328.16; 264/328.19;
264/328.4; 264/328.8; 264/401; 264/513; 425/130; 425/560; 428/120;
428/121; 428/122; 428/126; 428/192; 428/412; 428/542.8; 428/79 |
Current CPC
Class: |
B29C
45/1646 (20130101); B29C 45/1684 (20130101); B29B
2911/1402 (20130101); B29B 2911/14026 (20130101); B29B
2911/14086 (20130101); B29B 2911/14093 (20130101); B29B
2911/1412 (20130101); B29B 2911/14126 (20130101); B29B
2911/14146 (20130101); B29B 2911/14153 (20130101); Y10T
428/31507 (20150401); Y10T 428/24182 (20150115); Y10T
428/24198 (20150115); Y10T 428/24231 (20150115); Y10T
428/24777 (20150115); Y10T 428/1352 (20150115); Y10T
428/2419 (20150115) |
Current International
Class: |
B29C
45/16 (20060101); B32B 009/00 () |
Field of
Search: |
;428/120,79,122,121,35.7,126,131,195,36.7,542.8,192,60,412
;264/255,297.2,513,401,328.4,328.19,328.16,328.15,328.14,328.8
;425/130,560 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Ryan; Patrick
Assistant Examiner: Bahta; Abraham
Attorney, Agent or Firm: Davis and Bujold
Claims
We claim:
1. A process for coinjection molding a multi-colored decorative
article comprising the steps of:
a) metering an initial quantity of a molten first-colored
material;
b) supplying the initial molten first-colored material through a
supply gate in an injection mold cavity and into the cavity;
c) metering a quantity of molten second-colored material;
d) supplying the molten second-colored material through the supply
gate and into the cavity, contiguously with the initial
first-colored material;
e) controlling the locations of the first and second-colored
materials in the cavity, such that the initial first-colored
material is supplied to at least a desired first portion of the
cavity and the second-colored material is supplied to at least a
desired second portion of the cavity, by providing the first and
second-colored materials with desired melt viscosities, and
controlling the melt temperatures and rates of supply of the first
and second-colored materials.
2. A process according to claim 1, wherein the article is a
multi-colored preform suitable for blow molding a decorative
container, and further comprising the steps of:
providing a said injection mold cavity having a core pin therein to
define the preform between in inner surface of the cavity and an
outer surface of the core pin; and
steps b) and d), respectively, comprise supplying the first and
second-colored material through a gate centrally located at one end
of the cavity.
3. A process according to claim 2, wherein step e) comprises
providing the first-colored material with a first melt viscosity
and supplying the initial first-colored material at a first rate,
such that, as said first-colored material enters the cavity, the
initial first-colored material contacts and freezes to the inner
surface of the cavity and the outer surface of the core pin,
respectively forming exterior and interior surface layers of the
preform, with a volume of molten first-colored material being
defined between the outer surface layers.
4. A process according to claim 3, wherein:
step a) comprises, metering the initial quantity of first-colored
material, such that the initial first-colored material forms the
exterior and interior surface layers, defining the volume
therebetween, in only a proximate portion of the cavity adjacent
the gate, leaving a distal portion of the cavity remote from the
gate void of material.
5. A process according to claim 4, wherein:
step c) comprises, metering the second-colored material, such that
there is a sufficient quantity of the second-colored material to
completely fill the distal portion of the cavity only;
step d) comprises supplying the second-colored material
sequentially and contiguously following the initial first-colored
material; and
step e) comprises, providing the second-colored material with a
second melt viscosity, lower than the first melt viscosity, and
injecting the metered quantity of second-colored material at a
second rate, faster than the first rate, such that the
second-colored material passes through the volume and fills the
distal portion of the cavity.
6. A process according to claim 5, further comprising the steps
of:
metering a final quantity of the molten first-colored material,
such that there is a sufficient final quantity of the first-colored
material to fill the volume; and
supplying the final quantity of the first-colored material to the
cavity sequentially and contiguously following the metered quantity
of second-colored material, such that the final quantity of
first-colored material fills the volume, pushing substantially all
of the second-colored material out of the volume and into the
distal portion of the cavity.
7. A process according to claim 6, comprising providing a molten
relatively light-colored material as the first-colored material and
providing a molten relatively dark-colored material, compared to
the relatively light-colored material, as the second-colored
material.
8. A process according to claim 6, comprising providing a molten
relatively dark-colored material as the first-colored material and
providing a molten relatively light-colored material, compared to
the relatively dark-colored material, as the second-colored
material.
9. A process according to claim 4, wherein:
step c) comprises, metering the second-colored material, such that
there is a sufficient quantity of the second-colored material to
fill the distal portion of the cavity and to fill the volume;
step d) comprises supplying the second-colored material
sequentially and contiguously following the initial first-colored
material, such that the second-colored material fills the distal
portion and the volume.
10. A process according to claim 9, comprising providing a molten
relatively light-colored material as the first-colored material and
providing a molten relatively dark-colored material, compared to
the relatively light-colored material, as the second-colored
material.
11. A process according to claim 9, comprising providing a molten
relatively dark-colored material as the first-colored material and
providing a molten relatively light-colored material, compared to
the relatively dark-colored material, as the second-colored
material.
12. A process according to claim 3, comprising:
providing a molten relatively dark-colored material as the
first-colored material and providing a molten relatively
light-colored material, compared to the relatively dark-colored
material, as the second-colored material;
step a) comprises, metering the initial light-colored material,
such that the initial quantity of the light-colored material forms
the exterior and interior surface layers, defining the volume
therebetween, in a proximate portion of the cavity, adjacent the
path, and completely fills a distal portion of the cavity remote
from the path;
step c) comprises, metering the dark-colored material, such that
there is a sufficient quantity of the dark-colored material to
substantially fill the volume; and
step d) comprises supplying the dark-colored material sequentially
and contiguously following the initial light-colored material, such
that the second-colored material substantially fills the
volume.
13. A process according to claim 12, further comprising the step of
supplying a final quantity of the molten light-colored material to
the cavity, and metering the final quantity of light-colored
material such that the final quantity of light colored-material
fills a small void adjacent the path and clears the path of
dark-colored material in preparation for forming a next said
article in the cavity.
14. A process according to claim 2, wherein step e) comprises the
steps of providing the first-colored material and the
second-colored material with a melt viscosity and supplying the
first-colored material and the second-colored material at a rate,
such that, as the first and second-colored materials enter the
cavity, the materials flow through the cavity, with an
insubstantial amount of the materials freezing to the inner surface
of the cavity and the other surface of the core, and fill the
cavity from a distal end remote from the path, towards a proximate
end adjacent the path.
15. A process according to claim 14, wherein:
step a) comprises, metering the initial quantity of the
first-colored material, such that the first-colored material to
fills a distal portion of the cavity remote from the path only;
step c) comprises, metering the second-colored material, such that
there is sufficient quantity of the second-colored material to fill
at least a central portion of the cavity, adjacent the distal
portion and between the distal portion and the path; and
step d) comprises supplying the second-colored material
sequentially and contiguously following the initial first-colored
material, such that the second-colored material substantially fills
the central portion.
16. A process according to claim 15, wherein:
step a) comprises, metering the second-colored material, such that
the second-colored material substantially fills the proximate
portion of the cavity.
17. A process according to claim 16, further comprising the step
of:
supplying a final quantity of first-colored material to the cavity,
and metering the final quantity of first-colored material such that
the first-colored material fills a small void adjacent the path and
clears the path of second-colored material in preparation for
forming a next said article in the cavity.
18. A process according to claim 16, comprising providing a molten
relatively light-colored material as the first-colored material and
providing a molten relatively dark-colored material, compared to
the relatively light-colored material, as the second-colored
material.
19. A process according to claim 16, comprising providing a molten
relatively dark-colored material as the first-colored material and
providing a molten relatively light-colored material, compared to
the relatively dark-colored material, as the second-colored
material.
20. A process according to claim 2, comprising providing a desired
plurality of differently colored materials;
providing each of the plurality of materials with a melt viscosity
and supplying each of the plurality of materials a rate, such that,
as the materials enter the cavity, the materials flow through the
cavity, with an insubstantial amount of the materials freezing to
the inner surface of the cavity and the other surface of the core,
and fill the cavity from a distal end remote from the path, towards
a proximate end adjacent the path;
metering desired quantities of each of the differently colored
material in a desired sequence; and
sequentially and contiguously supplying each of the quantities, one
at a time, to the cavity in the desired sequence, thereby producing
a preform having a corresponding desired plurality of differently
colored bands in the desired sequence.
21. A process for coinjection molding a multi-colored decorative
article comprising the steps of:
a) metering an initial quantity of a molten first-colored portion
of a material;
b) supplying the initial molten first-colored portion through a
supply gate in an injection mold cavity and into the cavity;
c) metering a quantity of molten second-colored portion of the
material;
d) supplying the molten second-colored portion through the supply
gate and into the cavity, contiguously with the initial
first-colored portion;
e) controlling the locations of the first and second-colored
portions of the material in the cavity, such that the initial
first-colored portion of the material is supplied to at least a
desired first portion of the cavity and the second-colored portion
of the material is supplied to at least a desired second portion of
the cavity, by providing the first and second-colored portions of
the material with desired melt viscosities, and controlling the
melt temperatures and rates of supply of the first and
second-colored portions of the material.
22. A multi-colored article produced by a process comprising the
steps of:
a) metering an initial quantity of a molten first-colored
material;
b) supplying the initial molten first-colored material through a
supply path to an injection mold cavity having a core therein
defining the preform between an inner surface of the cavity and an
outer surface of the core;
c) metering a quantity of molten second-colored material;
d) supplying the molten second-colored material through the supply
path to the cavity, contiguously with the initial first-colored
material;
e) controlling the location of the first and second-colored
materials in the preform, such that the initial first-colored
material is supplied to a desired first portion of the cavity only
and the second-colored material is supplied to a desired second
portion of the cavity only, by providing the first and
second-colored materials with desired melt viscosities, and
controlling the melt temperatures and rates of supply of the first
and second-colored materials.
23. A multi-colored article produced by a process according to
claim 22, wherein said article is a preform suitable for blow
molding a decorative container.
24. A decorative container, blow molded from a multi-colored
preform produced by a process comprising the steps of:
a) metering an initial quantity of a molten first-colored
material;
b) supplying the initial molten first-colored material through a
supply path to an injection mold cavity having a core therein
defining the preform between an inner surface of the cavity and an
outer surface of the core;
c) metering a quantity of molten second-colored material;
d) supplying the molten second-colored material through the supply
path to the cavity, contiguously with the initial first-colored
material;
e) controlling the location of the first and second-colored
materials in the preform, such that the initial first-colored
material is supplied to a desired first portion of the cavity only
and the second-colored material is supplied to a desired second
portion of the cavity only, by providing the first and
second-colored materials with desired melt viscosities, and
controlling the melt temperatures and rates of supply of the first
and second-colored materials.
Description
FIELD OF THE INVENTION
This invention relates to coinjection molding of decorative (e.g.
multi-colored) articles, such as preforms for use in the blow
molding of decorative containers.
It is to be appreciated that the terminology of first and second
materials, as used herein, is intended to cover at least two
differently colored materials, preferably light-colored (or clear)
and dark-colored (or black), which are contiguously supplied, by a
coinjection process, to an injection mold, it being entirely
possible that one or more other materials may, by this process, be
sequentially or simultaneously, contiguously supplied before,
between, after, or at the same time as the first and second
materials. As used herein, clear and black are to be construed as
colors.
BACKGROUND OF THE INVENTION
Coinjection molding of preforms for use in blow molding is known in
the prior art. The formation of such containers is described in
detail, for example, in Applicant's U.S. Pat. No. 4,550,043. Both
single material preforms and multi-material preforms have been
injection molded in prior art multi-cavity molds, which may have as
many as 96 cavities, into which the material, from which the
preforms are to be formed, is injected simultaneously thereby to
simultaneously produce a preform in each of the cavities.
FIG. 1 is a diagrammatic illustration of a prior art mold in which
two different materials are sequentially and contiguously supplied
to a plurality of cavities through a common manifold system. The
manifold system of FIG. 1 and a process of using the system are
disclosed in Applicant's U.S. Pat. Nos. 5,040,963 and 5,221,507.
The prior art mold 1 illustrated in FIG. 1 defines a common
manifold arrangement 19 to convey both of the materials, which will
form the preform, to the cavities 3. It is known in such an
arrangement to repeatedly divide the material flow, whereby the
flow path 33, 35, 37 from the material inlet 33 of the mold 1 to
each cavity 3 is identical, whereby each cavity 3 will receive an
equal metered amount of material at substantially the same
temperature and at substantially the same time as every other
cavity 3.
Construction details of the mold 1, its manifold system 19, the
heating means 39 and the insulating means 41, together with the
cavity design 3, 7 and cooling arrangements for the core pins 5 and
cavities 3, the split neck rings 9, etc., are considered to be
conventional in this technology and will be readily apparent to
those skilled in the art. Similarly the plasticizer barrels 25 and
27 and ram pots 29 and 31 are of conventional construction, as are
the general engineering details of the diverter valves 21 and 23.
Accordingly these matters will not be described in detail in this
application.
With reference now to FIG. 2, there is diagrammatically illustrates
an interface between a first molten material 30 and a second molten
material 32 in hot runner 33 at X (See FIG. 1). For the sake of
illustration, it may be assumed that the first molten material 30
is supplied from plasticizer barrel 25 and the second molten
material 32 is supplied from plasticizer barrel 27. When the
diverter valves 21 and 23 have been operated to change the supply
of molten material from plasticizer barrel 25 and ram pot 29 to
molten material from plasticizer barrel 27 and ram pot 31, the
second molten material is supplied sequentially behind and
contiguously with the first molten material. Since the two
materials are supplied sequentially and contiguously, an interface,
as illustrated in FIG. 2, is formed between the two materials as
they travel through the hot runners. The hot runner 33 is
maintained at approximately 500.degree. F., and the frictional drag
on the material is illustrated at the interface or melt front of
the two materials.
The prior art injection molding techniques and manifold
arrangements, however, have only been proposed for the production
of preforms having multiple layers of different materials and have
not been proposed for the molding of preforms having differently
colored (including clear) areas for use in producing decorative
containers. Until the recent invention, the process parameters for
the injection of differently colored materials to produce
multi-colored preforms and resulting containers were not
understood.
SUMMARY OF THE INVENTION
Wherefore, it is an object of the present invention to provide a
coinjection process suitable for the production of multi-colored
preforms and resulting decorative containers.
The present invention provides a process for coinjection molding a
multi-colored decorative article comprising the following steps.
Metering an initial quantity of a molten first-colored material.
Supplying the initial molten first-colored material through a
supply gate in an injection mold cavity and into the cavity.
Metering a quantity of a molten second-colored material. Supplying
the molten second-colored material through the supply gate and into
the cavity, contiguously with the initial first-colored material.
Controlling the locations of the first and second-colored materials
in the cavity, such that the initial first-colored material is
supplied to at least a desired first portion of the cavity and the
second-colored material is supplied to at least a desired second
portion of the cavity, by providing the first and second-colored
materials with desired melt viscosities, and controlling the melt
temperatures and rates of supply of the first and second-colored
materials.
The present invention also provides a process as set forth above,
in which the molten second-colored material is supplied
sequentially or simultaneously, as well as contiguously with the
first-colored material.
The present invention also provides a multi-colored article
produced by the above process.
The present invention also provides a multi-colored preform,
suitable for blow molding a decorative container, produced by the
above process, and to a decorative container blow molded from such
a preform.
The present invention further provides a process for coinjection
molding a multi-colored decorative article comprising the following
steps. Metering an initial quantity of a molten first-colored
portion of a material. Supplying the initial molten first-colored
portion through a supply gate in an injection mold cavity and into
the cavity. Metering a quantity of a molten second-colored portion
of the material. Supplying the molten second-colored portion
through the supply gate and into the cavity, contiguously with the
initial first-colored portion. Controlling the locations of the
first and second-colored portions of the material in the cavity,
such that the initial first-colored portion of the material is
supplied to at least a desired first portion of the cavity and the
second-colored portion of the material is supplied to at least a
desired second portion of the cavity, by providing the first and
second-colored portions of the material with desired melt
viscosities, and controlling the melt temperatures and rates of
supply of the first and second-colored portions of the
material.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described, by way of example, with
reference to the accompanying drawings, in which:
FIG. 1 is a diagrammatic cross-section of a multi-cavity sequential
coinjection mold system according to the prior art;
FIG. 2 diagrammatically illustrates a cross-section of the junction
between two different molten materials being sequentially and
contiguously injected into the cavities, the cross-section being
taken immediately downstream of the diverter valves of the system
illustrated in FIG. 1 at arrow "X";
FIGS. 3 through 5 are diagrammatic cross-sections of one cavity of
the mold system illustrated in FIG. 1, showing the distribution of
materials in preforms formed therein according to first through
third embodiments, respectively, of the invention;
FIG. 6 is a graph plotting viscosity against shear rate for three
samples of PET with varying pigment loads;
FIG. 7 is a graph plotting viscosity against melt temperature for
three samples of PET with varying pigment loads; and
FIG. 8 is a diagrammatic elevation of a decorative bottle blow
molded from a preform according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
With reference now to FIG. 3, the sequence of injection of molten
materials for the formation of a multi-colored coinjected preform
according to a first embodiment of the invention will be described.
The preform and resulting container, according to the first
embodiment, both have a dark colored proximate or bottom portion B
and a light-colored (or clear) distal or top portion T.
At the beginning of an injection cycle according to the first
embodiment, an initial metered quantity of molten light-colored PET
45 is supplied to cavity 3 to flow therethrough to neck forming
portion 51. As the initial molten light-colored PET 45 flows
through the cavity 3, it meets the relatively cool core pin 5 and
relatively cool inner surface 7 of the cavity and freezes in
contact therewith, forming exterior 53 and interior 55 surface
layers of frozen light-colored PET 45 of the preform with a volume
57 of molten light-colored PET 45 flowing therebetween. The initial
quantity of light-colored PET 45 is metered so that there is a
sufficient quantity of light-colored PET 45 to completely fill the
desired top portion T of the cavity 3 and to form only the exterior
53 and interior 55 surface layers in the desired bottom portion
B.
When the metered quantity of molten light-colored PET 45 has been
supplied to the cavity 3, a desired quantity of molten dark-colored
PET 43 is supplied to the cavity 3. The molten dark-colored PET 43
is supplied sequentially and contiguously following the initial
metered quantity of molten light-colored PET 45. Thus, an
interface, similar to that illustrated in FIG. 2, exists between
the initial molten light-colored PET 45 and the molten dark-colored
PET 43. The metered quantity of molten dark-colored PET 43
contiguously follows the molten light-colored PET 45 through the
gate 17, into the cavity 3 and through the volume 57, pushing the
initial quantity of molten light-colored PET 45 before it. The
molten dark-colored PET 43 is metered such that it substantially
fills the volume 57 in the desired bottom portion B of the cavity
only and pushes the molten light-colored PET 45 out of volume 57
and into the desired top portion T of the cavity. In this manner,
the desired top portion T of the cavity is completely filled with
light-colored PET 45 only.
The quantity of molten dark-colored PET 43 is also metered so that
a next following final quantity of molten light-colored PET 45 will
flow through gate 17 and fill a small void 61 adjacent the gate 17,
in order to clear the hot runners and the gate 17 of molten
dark-colored PET 43 in preparation for production of the next
preform. Once the molten dark-colored PET 43 has been cleared from
the hot runners and the gate 17, the multi-colored preforms are
removed from the mold cavities 3 and the next injection cycle is
commenced using the remaining metered quantity of molten
light-colored PET 43, already present at the gates 17, as the
initial metered quantity of molten light-colored PET 45.
The quantity of dark-colored PET 43 may alternatively be metered
such that the dark-colored PET 43 completely fills the volume 57
and the initial quantity of light-colored PET 45 for producing the
next preform is present at the gate 17, but does not enter the
cavity. In this case, there is no final quantity of light colored
PET 45 and there is no small volume 61 filled by a final quantity
of light colored PET 45.
In the bottom portion B of the preform and resulting container
according to the first embodiment, the dark-colored PET 43 filling
the volume 57 masks the light-colored PET 45 defining the interior
55 and exterior 53 surface layers. The bottom portion B is
therefore seen as dark-colored.
A second embodiment of the invention will now be described with
reference to FIG. 4. The preform and resulting container according
the second embodiment have a dark-colored distal or top portion T1
and a light-colored proximate or bottom portion B1. The
dark-colored material and the light-colored material are again
preferably formed of the same resin, preferably PET, but they are
deliberately made dissimilar in melt viscosity and flow
characteristics via process conditions and additives. In
particular, the dark-colored PET 43 is provided with a
significantly lower melt viscosity, and is supplied at a higher
melt temperature and a faster rate than the light-colored PET
45.
The same injection sequence used in the first embodiment, i.e.
light-dark-light colored molten PET, is used to achieve a preform
according to the second embodiment. The metered quantity of the
initial molten light-colored PET 45, however, is reduced compared
to the metered quantity of the initial molten light-colored PET in
the first embodiment. Moreover, the initial molten light-colored
PET 45 is, in the preferred process, injected at a relatively slow
rate, preferably 3-50% slower than when filling the entire cavity 3
with a single material in the conventional fashion.
The initial molten light-colored PET 45 is injected at a relatively
slow rate to ensure that a substantial quantity of the initial
molten light-colored PET 45 freezes to the relatively cool core pin
5 and the relatively cool inner surface 7 of the cavity to define
interior 55 and exterior 53 layers of the preform with the volume
57 of molten material flowing therebetween, as previously
described. Moreover, the desired quantity of the initial molten
light-colored PET 45 is metered, so that there is only a sufficient
quantity of molten light-colored PET 45 to form interior 55 and
exterior 53 surface layers in the desired bottom portion B1 of the
preform, as illustrated in FIG. 4.
When the metered quantity of initial molten light-colored PET 45
has been supplied to the cavity 3, a desired quantity of molten
dark-colored PET 43 is sequentially and contiguously supplied to
the cavity 3. The quantity of molten dark-colored PET 43 is
injected at a relatively fast rate, preferably 3-50% faster than
when filling the entire cavity 3 with a single material in the
conventional fashion, and at a higher melt temperature than when
filling the entire cavity with a single material in the
conventional fashion.
The exterior 53 and interior 55 surface layers of light-colored PET
45 insulate the molten dark-colored PET 43 flowing in the volume 57
from the relatively cool core pin 7 and inner surface 7 of the
cavity. Since the molten dark-colored PET 43 is made less viscous,
supplied at a higher melt temperature, injected at a relatively
fast rate, and insulated from the relatively cool core pin and
cavity by the exterior 53 and interior 55 surface layers only, an
insignificant quantity of the molten dark-colored PET 43 freezes to
the frozen light-colored PET 45 which has formed the exterior 52
and interior 55 surface layers in the bottom portion B1 of the
preform, while the bulk of the molten dark-colored PET 43 flows
relatively easily over the frozen light-colored PET 53 and 55 in
the bottom portion B1 to fill the top portion T1. The molten
dark-colored PET 43 essentially "slides" through the volume 57,
contiguously with the initial molten light colored PET 45, to fill
the top portion T1 of the preform. The desired quantity of molten
dark-colored PET 43 is metered such that there is a sufficient
quantity of molten dark-colored PET 43 to fill the desired top
portion T1 of the preform, but not the volume 57 in the desired
bottom portion B1.
Once the metered quantity of molten dark-colored PET 43 has been
supplied to the cavity 3, a final quantity of molten light-colored
PET 45 is sequentially and contiguously supplied to the cavity 3.
The final quantity of molten light-colored PET 45 fills volume 57,
pushing substantially all of the molten dark-colored PET 43 out of
volume 57 and into the desired top portion T1. Thus, a preform and
resulting container that has a dark-colored top portion T1 and a
light-colored bottom portion B1 is formed.
Despite the use of a lower melt viscosity, higher melt temperature
and fast injection rate for the molten dark-colored PET 43, a
relatively small, insignificant quantity of the molten dark-colored
PET unavoidably freezes to the surfaces of the exterior 53 and
interior 55 surface layers in volume 57. As a result, when the
light-colored PET 45 is clear, the desired bottom portion B1 of the
preform according to the second embodiment will be seen as
light-colored, rather than clear. When the preform is blow molded
into the desired decorative container, however, the walls of the
preform are stretched and thinned to a large degree, for example,
by a factor of twelve. After being stretched to such a large
degree, the small quantity of dark-colored PET 43 is stretched so
thin that it becomes substantially invisible to the naked eye, and
the desired bottom portion of the resulting container is therefore
seen as clear.
In order to produce a preform and resulting container having a
light-colored top portion T1 and a dark-colored bottom portion B1
according to the second embodiment, the injection sequence is
reversed, i.e. the injection sequence becomes dark-light-dark
colored molten PET. In this manner the initial molten dark-colored
PET 43 forms the exterior 53 and interior 55 surface layers in the
bottom portion B1 only, the molten light-colored PET 45 flows
through the volume 57 and fills the top portion T1, and the final
quantity of molten dark-colored PET 43 fills the volume. The result
is a preform in which the colors are reversed from those shown in
FIG. 4.
If it is desired to blow mold a container having a dark-colored top
portion T1 and a light-colored bottom portion B1 of the same color
as the second embodiment, the preform may also be produced as
follows. The quantity of dark-colored molten PET 43 is metered such
the molten dark-colored PET 43 completely fills the top potion T1
and completely fills the volume 57 in the bottom portion, thereby
eliminating the final quantity of molten light-colored PET 43. The
resulting preform will be seen as a single dark color. However,
after blow molding the preform into the desired container, due to
the large degree of stretching of the preform discussed above, and
providing the layer of dark-colored material in the volume 57 is
thin enough, the dark-colored material in volume 57 will be
stretched so much that the bottom portion B1 will be seen as
light-colored.
A third embodiment of the invention will now be described with
reference to FIG. 5. The preform and resulting container according
the third embodiment have a light-colored distal or top portion T2,
a dark-colored central portion C, and a light-colored proximate or
bottom portion B2. The dark-colored material and the light-colored
material are again preferably formed of the same resin, preferably
PET, both of which, however, are provided with a significantly
lower melt viscosity, and supplied at a faster rate and a higher
melt temperature, than when filling the entire cavity 3 with a
single material in the conventional fashion.
A light-dark-light colored molten PET injection sequence is used to
achieve a preform according to the third embodiment. The desired
metered quantity of the initial molten light-colored PET 45,
however, is provided with the lower melt viscosity, and is injected
at the relatively high melt temperature and at the relatively high
rate, to ensure that the initial molten light-colored PET 45 flows
through the cavity 3, with only an insubstantial quantity of the
initial molten light-colored PET 45 freezing to the relatively cool
core pin 5 and surface 7 of the cavity. The temperature of the core
pin 5 and the cavity 3 may be elevated above the conventional
temperature to further ensure that an insignificant quantity of the
initial molten light-colored PET 45 freezes thereto. The quantity
of the initial molten light-colored PET 45 is metered so that only
the desired top portion T2 of the preform is filled with
light-colored PET 45, as illustrated in FIG. 5.
When the metered quantity of initial molten light-colored PET 45
has been supplied to the cavity 3, a metered quantity of molten
dark-colored PET 43 is sequentially and contiguously supplied to
the cavity 3. The quantity of molten dark-colored PET 43 is
injected at the relatively fast rate and at the relatively high
melt temperature, such that only an insubstantial quantity of the
molten dark-colored PET 43 freezes in the bottom portion B3 of the
preform. The quantity of molten dark-colored PET 43 is metered such
that only a desired central portion C of the preform is filled with
dark-colored PET 43.
Once the metered quantity of molten dark-colored PET 43 has been
supplied to the cavity 3, the next metered quantity of final molten
light-colored PET 45 is sequentially and contiguously supplied to
the cavity 3. The quantity of final molten light-colored PET 45 may
also be injected at the relatively fast rate and the relatively
high melt temperature. The final quantity of molten light-colored
PET 45 is metered such that the desired bottom portion B2 of the
preform is filled with light-colored PET 45, at which point in
time, the supply of molten PET is halted and the preform is cooled
and then removed from the mold.
By injecting each desired metered quantity of molten dark and
light-colored PET at the faster rate, the total manufacture time
for producing a set of preforms is advantageously reduced by 3-50%
than when filling the cavity 3 in the conventional manner. Given
proper selection and control of the temperature of the cavity 3 and
the core 5, however, the light and dark-colored PET 45, 43 may both
be provided with a conventional melt viscosity, and be injected at
a conventional rate and a relatively low or conventional melt
temperature.
The injection sequence of the third embodiment may be reversed,
i.e. dark-light-dark molten PET. If the sequence is reversed, the
final quantity of the molten dark-colored PET 45 may be provided
with a relatively low or conventional melt viscosity and be
injected at a relatively slow or conventional rate.
Any desired plurality of dark bands separated by light bands may be
formed in the preform according to the third embodiment. For
example, an injection sequence of dark-light-dark-light-dark molten
PET, would produce a preform and resulting container having the
same sequence of colored bands of material. Likewise, any desired
plurality of colors may be injected in any desired sequence. Three
different colors A, B, C, (red, white and blue, for example), may
be injected in any desired sequence to form a tri-colored
container. The injection sequence would then be A-B-C-A, with the
final quantity of color A serving as the initial quantity of color
A when forming the next preform.
In addition banded two color preforms may be produced by the
process of the third embodiment.
EXPERIMENT 1
Rheology tests using a parallel plate rheometer were performed on
three samples of molten PET containing varying loads of pigment
(holcobatch blue 932183). The three molten PET samples tested were,
a clear control sample A, a three percent pigment load B, and a
twelve percent pigment load C. The space between the plates was
filled with the three molten PET samples, and the plates were
rotated relative to each other at dynamic testing frequencies
providing a shear rate ranging from 1 to 100 (rad/s) at a set
temperature of 262.degree. C. for each sample. The viscosity of
each sample was measured throughout the full range of dynamic
testing frequencies and resulting shear rates. While shear rate is
increased in the plasticizer by way of appropriate control of
processing conditions, in the present invention increased shear
rate may be created by increasing the injection rate of molten PET
into the cavity.
The results of Experiment 1 illustrate the rheological trends which
take place as the amount of pigment in the PET is increase. FIG. 6
is a plot of the viscosity of the three samples A, B, and C of PET
over the shear rate (rad/s). It can be seen from FIG. 7 that the
viscosity in poise of the PET, indicated on the Y-axis in FIG. 6,
decreases with increased pigment loading. For example, at a
randomly chosen shear rate of 62 rad/s, indicated on the X-axis,
the viscosities of the three test samples A, B and C were 7,000,
3,500, and 1,800 poise, respectively. This holds true throughout
the dynamic testing shear rate range of 1 to 100 rad/s, and can be
assumed to follow that same trend at higher shear rates.
EXPERIMENT 2
In a second experiment, the viscosities of three different test
samples of molten PET, a clear D, a one percent pigment load E, and
a three percent pigment load F, were tested at a fixed shear rate
of 6 rad/s, while the temperature was decreased from 270.degree. C.
to 225.degree. C.
The viscosities of the three sample D, E and F are plotted over the
injection temperature of the samples in FIG. 7. As can be seen in
FIG. 7, as the temperature increases, the viscosities of the loaded
samples E and F decreases significantly compared to the non-loaded
clear sample D.
In conclusion, the viscosity of molten PET decreases with increased
pigment loading, as illustrated in FIG. 6. Moreover, the difference
between the viscosities of the relatively heavily pigment loaded
samples E and F and the that of non-loaded sample D increases as
the melt temperature increases, as illustrated by FIG. 7. It is
particularly noted that the viscosity of the loaded samples B, C, E
and F are nearly half that of the clear PET samples A and D, in the
normal pigment loading range of 0 to 3% within the conventional
injection temperature range of 240.degree. C. and above.
A molten PET that is heavily loaded with pigment has a lower
viscosity than a molten PET with a zero to light pigment loading.
Thus, the molten heavily loaded PET according to the invention is
provided with a relatively low viscosity compared to a molten
lightly loaded PET, simply by virtue of its relatively high pigment
load. Molten heavily loaded PET will slide relatively easily
through the cavity 3 or volume 57 with no significant freezing,
without requiring any additives or special process conditions to
decrease its viscosity. On the other hand, when it is desired to
decrease the viscosity of the molten lightly pigment loaded PET, it
is necessary to add well known additives to, increase melt
temperature of and/or increase shear rate of the molten lightly
loaded PET. When desired, the difference in viscosity between a
molten heavily loaded PET and a molten lightly loaded PET can be
increased by increasing the temperature and/or the shear rate of
the molten heavily loaded PET. Increasing the temperature and/or
shear rate of the molten heavily loaded PET also helps prevent the
molten heavily loaded PET from freezing to the inner walls of the
cavity or volume 57.
The prior art multi-cavity mold 1 and manifold system 19 for the
sequential coinjection molding of preforms illustrated in FIG. 1 is
a preferred system for producing preforms for use in blow molding
decorative containers according to the invention. However, other
known coinjection molding systems having a variety manifold
arrangements are capable of contiguously injecting two different
materials into a single, or plurality of mold cavities and may be
employed according to the present invention. For example,
coinjection systems having multiple hot runner manifolds that
contain a hot runner system for each of a plurality of different
materials to be supplied to the cavities are suitable for
practicing the present invention.
Some of these multiple hot runner systems have a valve at the gate
17 of each of the cavities 3 for controlling the supply of the
different materials, while others have concentric supply gates at
each of the cavities. When using a multiple manifold system having
concentric supply gates, the differently-colored materials may be
supplied simultaneously and contiguously and/or sequentially and
contiguously to the cavities. For example, a preform according to
the first embodiment, see FIG. 3, may be produced using concentric
supply gates by first supplying a first portion of the initial
metered quantity of light-colored PET 45, sufficient to fill the
top portion T, through the outer concentric gate. Through the use
of appropriately designed concentric supply gates, the metered
quantity of dark-colored PET 43 and the remaining portion of the
initial light-colored PET 45 may then be supplied simultaneously
and continuously with each other in order to form the bottom
portion B.
Further process of the present invention may be practiced using a
system that supplies a single material through a single manifold
system, the differently colored materials being created in such a
single material, single manifold system by mixing desired
quantities of differently colored pigments into the material before
or as the material enters the manifold system, as required, to
create metered portions of the material that are differently
colored.
It is to be appreciated that the first and second materials that
are used to form the multi-colored articles of the instant
invention, can be manufactured from two or more materials of
different melt viscosities. Melt viscosity differences of
approximately .+-.100%, or even more, are possible. In addition,
the temperature sensitivities and the coefficients of drag of the
molten resin materials used to mold the multi-colored article are
other important factors to consider in ensuring that the boundary
interface between two adjacent molten resin materials remains
intact and in ensuring that the molten materials slide through
and/or freeze to the cavity 3 and/or volume 57 as desired.
The multi-colored article can be formed from three or more
separate, sequentially injected materials or one of the materials
can be a blend of two or more resin materials, e.g. PET and
polyethylene naphathalate (PEN). PEN is a high barrier resin that
would be useful in achieving a longer shelf life of a container
which is manufactured according to the invention.
In the multi-colored preforms and resulting containers produced by
the present invention, the boundaries 70 between the dark 43 and
light-colored PET 45 are wavy, not straight, as diagrammatically
illustrated in a two-tone bottle in FIG. 8. A container having a
unique and decorative appearance is therefore produced by the
present invention.
The process of the present invention may by used to produce
articles other than preforms suitable for blow molding decorative
containers. The article produced in the cavity 3 may be a
decorative hollow article, such as a cap or closure for spray cans,
for example, with no need for a subsequent blow molding operation.
In which case, the cavity is defined by male and female mold parts.
Moreover, the article does not have to be hollow. The present
invention may be employed to produce decorative thin discs or
saucers that are planar, bowl shaped, wavy or any other desired
configuration.
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